This invention relates to the production of fire resistant structures, and more particularly to the production of such structures incorporating thermoplastic resins.
The use of thermoplastic resins in sheet form in construction (e.g., roofing) materials for buildings and vehicles of transport, especially ships, is of increasing interest by reason of the relatively light weight of such resins as compared with other materials used for the same purpose. Resinous construction materials generally are fiber-reinforced, as with glass mats.
A principal requirement of construction and maritime materials is fire retardancy. This has several aspects.
Fire propagation tendency is the tendency of the material to support combustion; i.e., to ignite. A test method for this property is ASTM procedure E1354 (oxygen consumption calorimeter test).
Fire retardancy is the tendency of the material to resist flame spreading. It can be evaluated by ASTM method E162.
Fire containment is the tendency of the material to serve as a fire barrier. Various heat release methods can be used for its evaluation.
Smoke and toxicity characteristics are related to the potential of escape from a burning area and for successful fire fighting. Smoke obscuration can be measured by ASTM method E662.
Fire endurance is the tendency of a material to maintain its structural integrity after a fire.
Fire containment in turn has several related parameters. They include flame spread, inherent flammability and heat conduction. If the material conducts enough heat to an adjacent space, ignition can occur. Thus, good fire containment is important for survivability. Containment can often be improved by reducing the thermal conductivity of the material.
A common approach to fire containment in the case of a thermoplastic is the use of a barrier layer, typically a ceramic, intumescent or ablative coating. A barrier layer can improve fire retardancy by reflecting the radiant heat back toward the source, by delaying heat penetration or by physically shielding the thermoplastic from the heat or flame source. As a result, the temperatures generated during burning are reduced, prolonging the survival of the thermoplastic resin and thereby improving its retention of mechanical properties.
Many types of previously known barrier coatings have serious disadvantages. For example, a ceramic coating of sufficient thickness to serve the purpose adds significant weight to the composite, rendering it unsuitable for nautical and many other applications. Intumescent paints, on the other hand, tend to adhere poorly to thermoplastic surfaces.
Accordingly, there is a need for improved barrier coatings to be used with thermoplastic building and construction materials, especially composites. A class of such improved coatings constitutes the present invention.